學用 ASP.Net 之 “字串” (5): StringBuilder 類

StringBuilder 類存在的理由是: 在對字串增刪改時, 比 string 類更快; 更快的原因是無須像 string 一樣反覆地釋放和重建.
但它會在需要時重新分配記憶體, 如果把需要的記憶體預製好, 它會更快.
StringBuilder 的屬性與方法:

/* 屬性 */Capacity;         // 容量; 可讀寫, 也可在構建時設定, 但改寫時使用 EnsureCapacity() 更保險Length;           // 長度; 可讀寫, 寫入 0 時, 同 Clear(); Length 

建構函式的 6 種重載:

using System.Text; // StringBuilder 所屬的命名空間 protected void Button1_Click(object sender, EventArgs e){    string str = "";    /* 無參時, Capacity 預設 16 */    StringBuilder sb1 = new StringBuilder();    str += sb1.Capacity.ToString("Capacity: #\n"); //Capacity: 16    /* 構建時指定 Capacity 大小 */    StringBuilder sb2 = new StringBuilder(11);    str += sb2.Capacity.ToString("Capacity: #\n"); //Capacity: 11    /* 使用字串構建時, 如果字串 Length > 16, 其 Capacity 同字串的長度 */    StringBuilder sb3 = new StringBuilder("abcdefghijklmnopqrstuvwxyz");    str += sb3.Capacity.ToString("Capacity: #\n"); //Capacity: 26    /* 指定 Capacity 和 MaxCapacity */    StringBuilder sb4 = new StringBuilder(4, 10);    str += sb4.Capacity.ToString("Capacity: #\t"); //Capacity: 4    sb4.Append("1234567890");    str += sb4.Capacity.ToString("Capacity: #\n"); //Capacity: 10    try { sb4.Append("ABC"); }    catch (Exception err) { str += err.Message + "\n"; } //容量小於當前大小...    /* 用字串構建, 同時指定 Capacity */    StringBuilder sb5 = new StringBuilder("1234567890", 32);    str += string.Format("Capacity: {0}\tLength: {1}\n", sb5.Capacity, sb5.Length); //Capacity: 32  Length: 10    /* 從字串截取構建, 同時指定 Capacity */    StringBuilder sb6 = new StringBuilder("ABCDEFG", 1, 3, 12);    str += string.Format("\"{0}\"\tCapacity: {1}\tLength: {2}", sb6, sb6.Capacity, sb6.Length); //"BCD"Capacity: 12Length: 3    TextBox1.Text = str;}

練習:

//ToString()protected void Button1_Click(object sender, EventArgs e){    StringBuilder sb = new StringBuilder("1234567890");    string s1 = sb.ToString();     //1234567890    string s2 = sb.ToString(2, 3); //345    TextBox1.Text = s1 + "\n" + s2;}//Append()、AppendFormat()、AppendLine()protected void Button2_Click(object sender, EventArgs e){    StringBuilder sb = new StringBuilder(256);    sb.Append("abcdefg");    sb.AppendLine();    sb.Append(3.1415926);    sb.AppendLine();    sb.AppendFormat("{0:#.##}", 3.1415926);    TextBox1.Text = sb.ToString();/*abcdefg3.14159263.14*/}//Insert()、Remove()、Replace()protected void Button3_Click(object sender, EventArgs e){    StringBuilder sb = new StringBuilder("..........", 256);    string s1 = sb.Insert(2, "ABC").ToString();  //..ABC........    string s2 = sb.Insert(2, 3.14).ToString();   //..3.14ABC........    string s3 = sb.Remove(6, 3).ToString();      //..3.14........    string s4 = sb.Replace('.', '*').ToString(); //**3*14********    TextBox1.Text = s1 + "\n" + s2 + "\n" + s3 + "\n" + s4;}//CopyToprotected void Button4_Click(object sender, EventArgs e){    string str = "..........";    char[] cArr = str.ToCharArray();    StringBuilder sb = new StringBuilder("1234567890");    sb.CopyTo(2, cArr, 0, 3);    TextBox1.Text = new string(cArr); //345.......}